The present invention relates to a control system for a dry-plate friction clutch of a motor vehicle, and more particularly to a system where a position of a pressure plate of the clutch is estimated in accordance with a desired speed for shifting the pressure plate.
A torque converter, an electromagnetic clutch and a mechanical dry-plate friction clutch are employed as a clutch for connecting or disconnecting an engine with a transmission of the motor vehicle. It has been proposed to provide a dry-plate friction clutch which is electronically controlled to be engaged for starting the vehicle and to be released before stopping of the vehicle
Japanese Patent Publication 62-47742 discloses a clutch control system where an engine speed changing rate at the start of a vehicle is detected to control the clutch. When the changing rate is positive, the clutch is operated to be engaged. When the changing rate is negative, the operation of the clutch is stopped to maintain the clutch at that position.
However, since the control system does not detect partial engagement of the clutch, the control of the clutch depends largely on the engine speed and the changing rate thereof. Namely, when the engine speed rapidly increases, the clutch is suddenly engaged, thereby causing hunting. On the other hand, when the engine speed gradually increases, the clutch is slowly operated from the disengagement state to the partial engagement state, which impairs starting characteristics.
Japanese Patent Application Laid-Open 59-124438 discloses a control system having a pressure plate position sensor for detecting the position of the pressure plate at the state of the engagement and the position at complete engagement. The pressure plate is shifted in each range divided by the positions at a speed predetermined for the range.
The provision of the pressure plate position sensor causes an increase in the manufacturing cost of the clutch.
Another problem is that an exact starting point of partial engagement is not detected when there is wear or a small thickness difference of the clutch plate.